vest 与 waistcoats 有什么区别?

查一下WIKIPEDIA,里面有解释的
Waistcoat
(a sleeveless under-jacket).This is called a waistcoat in the UK and many Commonwealth countries,or a vest in the US and Canada.It is often worn as part of formal attire,or as the third piece of a lounge suit.
Undershirt
(an undergarment,normally worn under a shirt).It is known as an undershirt in the US and Canada,vest in the UK and many Commonwealth countries,and singlet in Australia and Asia,and is typically in the form of a T-shirt or sleeveless top.